The following abbreviations as used throughout the following specification and in the claims have the meanings stated therefor.
BOD Biochemical Oxygen Demand.* PA0 COD Chemical Oxygen Demand.* PA0 COD.sub.C Colloidal chemical oxygen demand.* PA0 COD.sub.T Total chemical oxygen demand.* PA0 COD.sub.S Soluble chemical oxygen demand.* PA0 DO Dissolved Oxygen content.* PA0 MLSS Mixed Liquor Suspended Solids.* PA0 NH.sub.3 -N Ammonia Nitrogen.* PA0 NO.sub.3 -N Nitrate Nitrogen.* PA0 OUR Oxygen Uptake Rate, mg/gm VSS. PA0 PO.sub.4S Soluble Phosphate.* PA0 PO.sub.4T Total Phosphate.* PA0 HRT Hydraulic Retention Time, the residence time of a given batch or lot of sewage in a particular zone or system, expressed in minutes and hours. PA0 SS Settled Sludge.* PA0 SSV Sludge Settled Volume. PA0 TKN Total nitrogen as determined by the Kjeldahl method.* PA0 VSS Volatile Suspended Solids.* FNT * Concentrations expressed in milligrams per liter, mg/L, unless otherwise stated.
In treating wastewaters containing ammonia, it is known that certain aerobic autotrophic microorganisms can oxidize ammonia to nitrite and that nitrite can be further microbially oxidized to nitrate. This reaction sequence, viz., oxidation of ammonia to nitrate, is known in the art as nitrification and the responsible microorganisms are: Nitrosomonas and Nitrobacter. More specifically, Nitrosomonas are known to oxidize ammonia to nitrite in aqueous systems in which (1) dissolved oxygen levels are in excess of approximately 0.5 mg/l (as disclosed in H. E. Wild et al., "Factors Affecting Nitrification Kinetics," J. Wat. Pollut. Cont. Fed., 43, 1845-1854 (1971)) and (2) free ammonia in solution is held below about 10 to 150 mg/l (as disclosed in Anthonisen et al., "Inhibition of Nitrification by Ammonia and Nitrous Acid," J. Wat. Pollut. Cont. Fed., 43, 835-852 (1976)). Nitrosomonas microorganisms are ubiquitous in the environment, and seed for the development of a Nitrosomonas population in a sludge is therefore available from a wide variety of sources. Both Nitrosomonas growth rates and their ammonia-nitrogen oxidation reaction rates are a function of solution temperature, pH and dissolved oxygen levels. For example, a reaction rate of about 2.4 mg nitrogen oxidation per mg of microorganism per day at a temperature of 20.degree. C., a pH of 7.0 and a dissolved oxygen level of between 1 and 2 ppm has been reported. (See G. M. Wong-Chong, "Kinetics of Microbial Nitrification as Applied to the Treatment of Animal Wastes," Ph.D. Thesis, Cornell University, 1974.)
Further, Nitrobacter are known to oxidize nitrite to nitrate in aqueous systems where the dissolved oxygen level is in excess of approximately 0.5 mg/l (see H. E. Wild et al., supra) and free ammonia in solution is held below about 0.1 to 10 mg/l and free nitrous acid in solution is held below about 0.2 to 2.8 mg/l (see Anthonisen et al., supra). Nitrobacter microorganisms are ubiquitous in the environment also and seed for development of a Nitrobacter population in a sludge is therefore available from a wide variety of sources. Both Nitrobacter growth rates and their nitrite reaction rates are a function of solution temperature, pH and dissolved oxygen levels. For example, a reaction rate of about 7.0 mg nitrogen oxidation per mg of microorganism per day at a temperature of 20.degree. C., a pH of 7.0, and a dissolved oxygen level of between 1 and 2 ppm has been reported (see Wong-Chong, supra).
Complete elimination of ammonia entails the oxidation to nitrite and/or nitrate followed by reduction of the nitrite and/or nitrate to nitrogen gas. This latter reduction of the nitrite and/or nitrate to nitrogen gas is generally known in the art as denitrification and the reaction of reduction of nitrite and/or nitrate to free nitrogen is mediated by facultative heterotrophic microorganisms generally of the genera of Pseudomonas, Achromobacter, Bacillus and Micrococcus. These microorganisms are capable of oxidizing organic matter by utilizing oxygen and, in the absence of oxygen, they can use nitrite and/or nitrate, if present. Facultative heterotrophic microorganisms are further ubiquitous in the environment, and seed for development of populations in a sludge is therefore available from a variety of sources. Facultative heterotrophic microorganism growth rates and denitrification reaction rates and a function of solution temperature, pH and ratio of dissolved oxygen to nitrite/nitrate oxygen availability. For example, a denitrification reaction rate of about 0.6 mg nitrogen oxidation per mg of microorganism per day with methanol as an organic at a temperature of 20.degree. C. and a pH of 8 to 9 in the absence of dissolved oxygen has been reported (see R. P. Michael, "Optimization of Biological Denitrification Reactors in Treating High Strength Nitrate Wastewater," M. S. Thesis, University of Vermont, May 1973).
Frequent references are also made in the literature to unexplained nitrogen losses from basically aerobic sludges (e.g., as disclosed in K. Wuhrmann, "Effect of Oxygen Tension on Biochemical Reactions in Sewage Purification Plants" in "Advances in Biological Waste Treatment," W. W. Eckenfelds, Jr. and B. J. McCabe, Eds., Pergamon Press (1963); Barth et al., "Nitrogen Removal by Municipal Wastewater Treatment Plants," J. Wat. Pollut. Cont. Fed., 38, 7 (1966); and D. C. Climenhage, "Nitrogen Removal for Municipal Wastewater," Project No. 72-5-15, Ontario Ministry of the Environment (1975)). It has been speculated that these losses are due either to spurious amounts of "anaerobic" denitrification which occur in random localized "dead spots" in the sludge where dissolved oxygen levels have fallen to zero or to "aerobic" denitrification. In fact, in 1977, the inventor of the invention described and claimed herein speculated that "aerobic" denitrification does occur and is favored by high microbial sludge concentrations, low dissolved oxygen levels of about 1 ppm and a solution pH of 7.0 (see G. M. Wong-Chong et al., "Advanced Biological Oxidation of Coke Plant Wastewaters for the Removal of Nitrogen Compounds," Carnegie-Mellon Inst. of Research Report to the American Iron and Steel Institute, (Apr. 1977)). As a theoretical explanation, Wong-Chong, supra, postulated a porous microorganism particle model with oxygen gradients such that some portion of the core of the basically aerobic particle is anoxic. Others have speculated similarly regarding the existence of "aerobic" denitrification. (See, for example, L. B. Wood et al., "Some Observations on the Biochemistry and Inhibition of Nitrification," Water Research, 5, 543-551 (1981); I. Murray et al., "Interrelationships between Nitrogen Balance, pH and Dissolved Oxygen in an Oxidation Ditch Treating Farm Animal Waste, Water Research, 9, 25-30 (1975); and J. P. Voets, et al., "Removal of Nitrogen from Highly Nitrogenous Wastewaters," J. Wat. Pollut. Cont. Fed., 47, 394-398 (1975)).
The above biologically mediated processes of nitrification and denitrification, and conversion of ammonia to free nitrogen using Nitrosomonas, Nitrobacter and facultative microorganisms are well known. However, there is a large economic incentive for improvements in conventional approaches to treating wastewater containing high levels of ammonia and other contaminants. Research and development to upgrade the performance of biological treatment systems to handle high ammonia strength liquors has been extremely limited and has been basically considered unsuccessful.
With the exception of the speculations discussed above on how "aerobic" denitrification could possibly occur, all of the other prior art basically discredits the serious possibility of controllably achieving simultaneous nitrification and denitrification from a single sludge. In fact, the prior art has basically set forth that nitrification/denitrification conditions are thermodynamically antagonistic and as such, nitrification should be separated from denitrification (see Bishop et al., "Single-stage Nitrification-Denitrification," J. Wat. Pollut. Cont. Fed., 48, 521-531 (1976)).
Numerous possible permutations and combinations, which can be logically considered of multi-reaction step nitrification/denitrification systems, have been postulated in the literature. These, however, have been largely for application to the processing of low ammonia strength municipal sewage waste (see Bishop et al., supra; Climenhage, supra, Barth et al., "Chemical-Biological Control of Nitrogen and Phosphorus in Wastewater Effluent," J. Wat. Pollut. Cont. Fed., 40, 2040-2054 (1968); and J. L. Barnard, "Biological Nutrient Removal Without the Addition of Chemicals," Water Research, 9, 485-490 (1975)). Only two literature references are known (see Barker et al., "Biological Removal of Carbon and Nitrogen Compounds from Coke Plant Wastes," EPA Report EPA R2-73-167 (Apr. 1973); and P. D. Kostenbader et al., "Biological Oxidation of Coke Plant Weak Ammonia Liquor," J. Wat. Pollut. Cont. Fed., 41, 199-207 91969)) in which high strength ammonia containing wastewater was treated and of these only Barker et al., supra, attempted to achieve nitrification and denitrification. All other attempts to achieve nitrification or a combination of nitrification and denitrification, including that of the inventor herein prior to this invention, have been performed on weak-ammonia coke plant wastewater, i.e., wastewater from a coke plant from which a significant fraction of the ammonia has been stripped. High nitrification efficiencies for ammonia-stripped coke wastewater in a one-stage biological reactor with extended solids residence times has been reported (see A. Bhattacharyya et al., "Solids Retention Time--A Controlling Factor in the Successful Biological Nitrification of Coke Plant Waste," Proc. 12th Mid-Atlantic Industrial Waste Conference, Bucknell University, Lewisburg, Pa. (July 1980)).
Further, variable success with a two-stage nitrification-denitrification reactor system on ammonia-stripped coke wastewater has also been reported (T. R. Bridle et al., "Biological Treatment of Coke Plant Wastewaters for Control of Nitrogen and Trace Organics," Presentation at 53rd Annual Water Pollution Control Federation Conference, Las Vegas (Sept. 1980)). Moderate success in nitrifying ammonia-stripped coke wastewater has also been reported by the inventor of the invention described and claimed herein (see Wong-Chong et al., supra). Variable success has also been reported on a two-stage nitrification-denitrification reactor system on ammonia-stripped coke wastewater (see S. G. Nutt et al., "Two Stage Biological Fluidized Bed Treatment of Coke Plant Wastewater for Nitrogen Control," Presentation at the 54th Annual Water Pollution Control Federation Conference, Detroit (Oct. 1981)).
After experimental attempts to biologically treat coke wastewaters containing high ammonia concentrations directly, Kostenbader et al., supra, in experimental work to establish at what ammonia concentrations performance of microorganisms on wastewaters containing cyanide, thiocyanate and COD was affected, concluded that ammonia concentrations in excess of about 2,000 mg/l seriously inhibited the overall performance of biological sludge. In an extremely complex three-stage reaction system (two aerobic stages in series followed by an anaerobic stage), Barker et al., supra, treated high strength coke plant wastewaters for 352 days. Unfortunately, this program led to unsuccessful results. Typical feed ammonia strengths achieved during these experiments were less than 300 mg/l of ammonia (corresponding to about 12-fold dilution of the raw ammonia-containing feed wastewater to be treated) with substantially less that complete nitrification and denitrification. Highest feed ammonia strengths achieved were about 1200 mg/l ammonia (corresponding to a 3-fold dilution with respect to the raw wastewater feed). Treatment at these levels was sustained only for a single two-week period in the entire test program. Highest nitrification and denitrification rates achieved during this relatively high ammonia strength test period were only between 10% and 50%. In view of the results obtained, the project was abandoned.
Good sludge settleability is basic to the proper operation of all activated sludge systems. Activated sludge batch reactor technology can achieve high nitrogen removal through a predominantly co-current nitrification-denitrification reaction environment (Goronszy, M. C., "Single vessel intermittently operated activated sludge for nitrification-denitrification," 51st Wat. Pollut. Cont. Fed. Conf., Anaheim, U.S.A. (1978); Goronszy, M. C., "Intermittent operation of the extended aeration process for small systems," J. Wat. Pollut. Cont. Fed., 51,274 (1979); Goronszy, M. C. and Irvine, R. O., "Nitrification-denitrification in intermittently aerated activated sludge systems and batch systems, Proc. USEPA International Seminar on Control of Nutrients in Municipal Wastewater Effluents, 3, 74-117, San Diego, U.S.A. (1980). In so doing, the biomass is exposed to repeated sequences of varying high and low substrate tension (carbon and oxygen) on both macro and micro scales which affect the metabolic reaction pathways. A high biomass substrate storage capacity, through enzymatic transfer mechanisms, is necessary for the control of many species of microorganisms that can contribute to sludge bulking as well as for effective biological phosphorus removal.
Experiments conducted on biomass grown under substrate gradient loading conditions demonstrated experimentally identical soluble substrate uptake (as BOD) and associated specific oxygen utilization response under equivalent aerobic and anoxic-anaerobic floc-loadings (Goronszy, M. C., Barnes, D. and Irvine, R. L., "Intermittent biological waste treatment systems--process considerations," Water, AlChE Symp. Ser., 44, 129-136, (1980). Floc-loading and soluble substrate removal for various wastewaters relative to biological selectivity and sludge bulking control has been correlated (Goronszy, M. C. and Eckenfelder, W. W., "Floc-loading biosorption criteria for the treatment of carbohydrate wastewaters," Proc. 41st Annual Indust. Waste Conf., Purdue University, Indiana, U.S.A. (1986)).
Up to 95% nitrogen removal performance has been demonstrated in full scale cyclically operated batch facilities using cycles of 3 to 8 hours incorporating up to 50% of the cycle as a feed, non-mix, non-react sequence. The relative air-off fraction and subsequent mixing and aeration sequencing was shown to impact upon sludge settlement. It was also shown that anoxic mixing sequences, where soluble substrate concentration and an associated biomass oxygen utilization rate were low, caused a rapid development of sludge bulking conditions. Cyclically operated activated sludge systems generate satisfactory sludge settlement characteristics when operated for carbon removal and nitrification and denitrification.
Biological phosphorus removal is achieved through the selective growth of phosphate accumulating bacteria through the proper allocation of readily degradable soluble substrate to properly sequenced (temporal or spatial) anaerobic-aerobic reaction conditions. This mechanism is also common to sludge-bulking control requirements where residual soluble substrate availability is a major determining factor to filamentous growth. The major difference between that aerobic removal of soluble substrate results in filamentous sludge bulking control, while anaerobic removal of soluble substrate results in biological phosphorus removal while also providing a mechanism for sludge bulking control. To maintain an efficient balance for the two functions, it is necessary to provide substrate storage capacity to meet maximum intended phosphorus removal. These parameters have a variable inter-relationship due to out-of-phase diurnal variations in soluble organic and nutrient input parameters (FIG. 1).
Introduction of nitrate to the anaerobic zone also impacts upon availability of soluble substrate for storage to the amount of about 5 mg COD/mg NO.sub.3 -N whereby the subsequent aerobic uptake of soluble phosphorus is retarded by the amount of soluble substrate lost for the enzymatic transfer storage reaction. The presence of nitrate also causes an uptake of phosphate concurrently with carbon storage. Other forms of "oxygen" recharge to the anaerobic zone (e.g. H.sub.2 S) should also be avoided. Anaerobic release of phosphate by substrates that are not carbonaceous is deleterious as the release is not accompanied by an equivalent storage which is necessary for the aerobic uptake sequence. Phosphate uptake has been reported with nitrate in solution (Comeau, V. Rabinowitz, B. Hall, K. J. and Oldham, W. K., "Phosphate release and uptake in enhanced biological phosphorus removal from wastewater," J. Wat. Pollut. Cont. Fed., 59, 707-715 (1987). Operation with denitrifying bio-phosphorus storing bacteria means that co-current phosphate uptake and denitrification can take place in an aerobic zone or sequence.
Biological phosphorus removal has been obtained in fill-and-draw activated sludge operation with sequenced operation to provide the aerobic-anoxic-anaerobic reaction conditions (Ketchum, L. H., Irvine, R. L., Breyfogle, R. E. and Manning, J. F., "A comparison of biological and chemical phosphorus removal in continuous and sequencing batch reactors," J. Wat. Pollut. Cont. Fed., 59, 13-18 (1987). Total operating cycle times of 8.6 hours demonstrated typical phosphorus removal of 3.9 mg/L (4.3 mg/L reduced to 0.4 mg/L) and ammonia removal of 10 mg/L (25 mg/L reduced to 15 mg/L). Considerable phosphorus removal scatter was reported with high observations averaging 1.8.+-.0.75 mg/L above a mean of 0.63 mg/L. Manning, J. F. and Irvine, R. L., "The biological removal of phosphorus in a sequencing batch reactor," J. Wat. Pollut. Cont. Fed., 57, 87-94 (1985) showed the causation of sludge bulking in a batch reactor operated for enhanced biological phosphorus removal could be related to the duration of the anaerobic sequence.
Van Niekerk, A. M., Jenkins, D. and Richard, M. G., "The competitive growth of Zoogleal ramigera and type O2IN in activated sludge and pure culture--A model for low F/M bulking," J. Wat. Pollut. Cont. Fed., 59, 262-273 (1987), demonstrated that the actual soluble substrate concentration available to a mixed culture, rather than an average concentration over 24 hours determined the dominance of floc-former growth in that culture. Specifically Van Nickerk showed that the fate of soluble degradable organics (soluble COD) in wastewater was deterministic to the predominance of type O2IN in an activated sludge. Shao, T. J., "The mechanism and design of anoxic selectors for the control of low F/M filamentous bulking," Ph.D dissertation, University of California, Berkeley, U.S.A. (1986) has similarly shown in the impact of soluble COD availability on biological selectivity. The presence of soluble COD and its effect on sludge volume index is graphically demonstrated in FIG. 2. Wanner, J., Ottova, V. and Grau, P., "Effect of an anaerobic zone on settleability of activated sludge," Proc. IAWPR Cont., Rome, Italy 155-164 (1987) showed that the growth of Type O2IN, Sphaerotilus natans and Thiothrix can be effectively suppressed in systems with anaerobic initial reaction zones provided most of the available substrate is removed under anaerobic conditions. They also showed the selection pressure for these organisms was based on differences in metabolism between filamentous and non-filamentous microorganisms implying that there is no need for a substrate gradient in the anaerobic zones although phosphorus climination can be enhanced by providing a compartmentalized anaerobic zone. The need for an anaerobic substrate gradient for the control of Thiothrix filamentous bulking was also demonstrated.
Following the early work of Chudoba et al., (1973) Goronszy (1977) incorporated a biological selector zone into full-scale continuous inflow sequencing batch activated sludge systems using a transverse partial baffle wall at the inlet end of the reaction basin which formed two zones in continuous fluid communication. While effective filamentous sludge bulking control was demonstrated in over 40 facilities (both industrial and municipal) sludge bulking conditions have been shown to occur in a number of municipal systems (Goronszy, M. C., "Nitrogen removal and sludge bulking control in cyclically operated activated sludge systems," Ohio Wat. Pollut. Cont. Assoc. Conf., Akron, U.S.A. (1987).